The Leclanchè cell, which uses an amalgamated zinc anode, an electrolyte of ammonium and zinc chloride dissolved in water, and a manganese dioxide cathode, was first introduced in the 1860s. Since then, manganese dioxide has been used extensively in primary, single-use battery cells and particularly in dry and alkaline manganese dioxide zinc cells. Manganese dioxide has also been employed in various rechargeable batteries, including non-aqueous electrolyte cells having an alkali light metal such as lithium as an active material.
Battery grade manganese dioxide has been derived from naturally occurring manganese dioxide and synthetically produced manganese dioxide. Synthetic dioxide is generally divided into two categories: electrolytic manganese dioxide (EMD) and chemical manganese dioxide (CMD). Because of its high impurity content, naturally occurring manganese dioxide is not generally employed in alkaline or lithium cells. EMD, which is typically manufactured from direct electrolysis of a bath of manganese sulfate and sulfuric acid, is typically a high purity, high density, gamma-manganese dioxide that has been proven to be desirable for use as cathode active material in alkaline and lithium cells. During the electrolysis process, the gamma-EMD is deposited directly on the anode which is typically made of titanium, a lead alloy, or carbon. The EMD deposit is removed from the anode, crushed, ground, washed, neutralized and dried prior to use as an active material in a battery.
Electrolytic manganese dioxide has been a preferred material for use as the cathodic reactant in batteries primarily because of the ability of EMD to provide batteries having significantly improved discharge capacity compared to batteries produced from naturally occurring or chemically produced manganese dioxides. It is generally believed that the improved performance of EMD depends to a large extent on the operating conditions employed during the electrolysis process used to manufacture this material. The published literature teaches that among the more important operating conditions affecting the discharge capacity of a battery is the purity of the electrolyte used in the electrolysis. In fact, the published literature teaches that in order to improve the storage capacity of a battery, it is essential to use electrolytic manganese dioxide that does not contain significant heavy metal impurities. Another factor which is significant to the performance of a battery having an electrode comprised of EMD is the amount of active material present in the battery. In general, it is desirable for the battery to contain as much manganese dioxide as possible within a limited space to provide improved performance. Accordingly, attempts to improve the performance of batteries containing an electrode comprised of EMD have focused on manufacturing techniques that provide highly pure EMD and which provide EMD that can be packed into a high density form.
Other attempts to improve the service performance of alkaline batteries employing manganese dioxide active material include physically blending the manganese dioxide with an additive. Examples of such additives include titanates, such as BaTiO3 or K2TiO3, SnO2, Fe2O3—TiO2, TiO2 and Nb2O5.